I just heard a tape from Rabbi Yosef Chaim Greenwald saying that the Divrei Chaim of Sanz said that on Chanukah a person can do Teshuvah even on aveiros that the Zohar says that one cannot do Teshuvah on, because when the King comes to visit the jail, everyone can ask for anything.
(Lighting below 10 Tefachim where the Sh'chinah never goes, symbolizes how the King comes to visit even the darkest and lowest places on Chanukah...)